RU2759146C1 - Method for manufacturing biaxially textured substrate in the form of copper-nickel-based triple alloy tape for epitaxial deposition of buffer and high-temperature superconducting layers on it - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular to methods for obtaining biaxially textured substrates for epitaxial deposition of buffer and high-temperature superconducting layers on it for tape high-temperature superconductors (HTS) of the second generation. A method for manufacturing biaxially textured substrate in the form of copper-nickel-based triple alloy tape for epitaxial deposition of buffer and high-temperature superconducting layers on it includes smelting with the introduction of a niobium, or molybdenum, or tungsten alloying element into a copper-nickel alloy to obtain a copper-nickel-based triple alloy ingot, forging the ingot into a workpiece in the form of a rod, cold reversible rolling of the workpiece to a degree of deformation of ≥97% with obtaining a tape, and recrystallization annealing of the resulting tape at a temperature of ≥1000°C. At the same time, a triple alloy is smelted, at. %: niobium ≤2.5, or molybdenum ≤2.0, or tungsten ≤2.0, nickel - 40-45, copper - the rest.

EFFECT: high strength and sharpness of crystallographic texture are obtained, while maintaining non-magnetism at the operating temperature of the superconductor of 77 K.

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Description

The invention relates to metallurgy, in particular to methods for producing biaxially textured substrates.

The biaxially textured substrate serves as the basis for epitaxial deposition of buffer and high-temperature superconducting (HTSC) layers on it. The finished multilayer tape can be used to transmit electricity with the lowest losses, to create strong magnetic fields in helium-free HTSC solenoids, to design cost-effective, with improved weight and size characteristics of products for the electric power industry and medical equipment. In addition, an HTSC wire, in which a biaxially textured substrate tape is used, is the only material that makes it possible to create ultrahigh magnetic fields necessary for the implementation of a thermonuclear fusion reaction in compact tokamaks.

In the 90s. the technology of high-temperature superconducting cables of the second generation was developed, based on the epitaxial deposition of a ceramic high-temperature superconductor (HTSC) through buffer layers on a biaxially textured metal substrate [Goyal A., Norton DP, Budai JD, Phavantham N., et. al. High Critical Current Density Superconductors Tapes by Epitaxial Deposition of YВа _{2 Сu 3} О _х Thick Films on Biaxially Texturated Metals // Appl. Phys. Lett. 1996. V.69, No. 16. P.1795-1797], which led to the need to obtain metal substrate tapes with a high degree of perfection of cubic texture {100} <001>.

The main characteristic of tape multilayer HTSCs is the value of the critical current, which is largely determined by the sharpness of the crystallographic texture in the superconductor material, inherited from the biaxial cubic texture of the metal substrate. It is also desirable that the metal substrate is not ferromagnetic at the operating temperature of the HTSC, since the lower the magnetic permeability of the substrate, the greater the critical current.

For the production of long strips in industry, it is necessary to have sufficiently high strength properties of the supporting metal strip, which ensures the structural integrity of the HTSC layer. In addition, it is desirable that the substrate tape, in addition to a high degree of texture, non-magnetic, and strength, has a high resistance to oxidation, especially at the deposition temperatures of the buffer and superconducting layers.

Therefore, the creation of a method for the manufacture of a biaxially textured substrate from a ternary alloy on a copper-nickel base, which has high strength properties of a supporting metal strip and thereby expands the line of ternary alloys on a copper-nickel base, possessing the necessary strength properties and a degree of sharpness of the crystallographic texture, while maintaining non-magnetic at the operating temperature of a high-temperature superconductor (77 K), inherent in substrates of a ternary alloy on a copper-nickel base with additions of iron, or chromium, or vanadium is a technical problem to be solved by the claimed technical solution.

The substrate can be textured using deformation processes such as cold rolling and subsequent recrystallization annealing of the substrate.

A known method of manufacturing a biaxially textured substrate, including smelting, forging, cold rolling and subsequent recrystallization annealing, which uses various pure metals: Ni, Cu, Pd, Pt, Ag and some alloys of these metals [US Patent No. 6,180,570].

The listed pure metals have an extremely low value of the yield stress in the textured state (from 25 to 35 MPa). In addition, in the described method of manufacturing a substrate, not all metals provide, after appropriate technological procedures, the formation of a sharp cubic texture and the required level of strength. For example, in silver when rolling at room temperature, a texture of deformation of such a component composition is formed that it becomes impossible to obtain a cubic texture of recrystallization during subsequent annealing [Wasserman G., Grevin I. Textures of metallic materials. M .: metallurgy, 1969. 655 p.]. In pure copper, as well as in pure nickel, after high degrees of cold rolling, a texture of such a component composition is formed, which ensures the formation of a sharp cubic texture in the strip after primary recrystallization, but low strength properties do not allow the production of extended strips.

Thus, this method of manufacturing a biaxially textured substrate does not ensure the achievement of high strength properties of the carrier metal tape while maintaining non-magnetic properties at the operating temperature of the high-temperature superconductor, and, therefore, does not solve the technical problem.

A known method for the production of biaxially textured substrate, including smelting, forging, cold reverse rolling to a degree of deformation of more than 97% and recrystallization annealing at a temperature of ≥1000 ° C, which uses various ternary alloys based on nickel. [US Patent 5,964,966]. Examples of such alloys are alloys with 5-10 at. % W and 2-4 at. % Al. Alloy Ni-5% W-2% Al has a high degree of perfection of crystallographic texture and required strength, but nickel is a strong ferromagnet and the alloy has a Curie temperature of about 260 K, i.e. at 77 K, the operating temperature of the HTSC, is ferromagnetic. Since the magnitude of the critical current in the superconducting layer is affected by the magnetic state of the substrate material (the lower the magnetic permeability of the substrate, the greater the critical current), it is necessary that the substrate material be nonmagnetic at the operating temperature of the HTSC. In order to achieve a non-magnetic state of a ternary nickel alloy, the amount of alloying elements introduced is increased. The obtained alloys Ni-5% W-2% Al and Ni-5% W-4% Al are nonmagnetic at 77 K, but they fail to obtain the required degree of perfection of the cubic texture due to a decrease in the energy of stacking faults in the alloy below the threshold value, at which in the alloy after cold deformation by rolling and subsequent recrystallization annealing, the formation of a sharp cubic texture is possible.

Thus, this method of manufacturing a biaxially textured substrate does not allow for the simultaneous fulfillment of two necessary conditions, namely, a perfect cubic texture while maintaining non-magnetism at the operating temperature of a high-temperature superconductor, and, therefore, does not solve a technical problem.

There is also known a method of manufacturing a biaxially textured substrate from a copper-nickel alloy, including smelting, forging, cold reverse rolling to a degree of deformation of more than 95% and recrystallization annealing at a temperature of ≥800 ° C, in which binary alloys are used as a copper-nickel alloy containing copper from 30 to 55 at. %, the preferred of which is a binary alloy Ni-55 at. % Cu [US Patent 5,964,966]. This copper-nickel alloy has a three-fold hardening (σ _0.2 ) in comparison with pure copper.

However, the desire to reduce the thickness of the metal substrate in order to reduce the weight of the structure of the HTSC wire dictates the need to further increase the strength of the tape. An increase in the strength of a copper-nickel alloy due to an increase in the nickel content in it is impossible, since the nickel content is 45-46 at. % is the limiting value for maintaining the paramagnetic state of the alloy (nonmagnetic at a liquid nitrogen temperature of 77 K). Therefore, it is not possible to achieve the required level of strength using double copper-nickel alloys, and thereby solve the technical problem.

Known close to the claimed technical essence of a method of manufacturing a biaxially textured substrate from a ternary alloy on a copper-nickel base - constantan, including smelting, forging, cold reverse rolling to a degree of deformation of more than 95% and recrystallization annealing at a temperature of ≥900 ° C [Varanasi CV, Brunke L., J Burke, Maartense I., Padmaja N., Efstathiadis H., Chaney A. and Barnes PN Biaxially textured constantan alloy (Cu 55 wt%, Ni 44 wt%, Mn 1 wt%) substrates for YBa ₂ Cu ₃ O _7-x coated conductors // Supercond. Sci. Technol. 2006. V. 19. P. 896-901.] This alloy in composition is close to the industrial constantan Cu-43% Ni-1.5% Mn (American standard C - 72150).

However, the introduction of such a third element as manganese into the copper-nickel base does not provide advantages from the point of view of alloy hardening. Manganese present in industrial constantan is a technological additive in the deoxidation of liquid metal during smelting [MV Maltsev, TA Barsukova, FA Borin. Metallography of non-ferrous metals and alloys. M .: GNTI on ferrous and non-ferrous metallurgy, 1960.372 p. (p.15)]. Consequently, the manganese present in this ternary alloy on a copper-nickel base does not allow achieving the required level of strength, and thereby solve a technical problem.

The closest to the claimed technical essence is a method of manufacturing a biaxially textured substrate from a ternary alloy on a copper-nickel base with the addition of 3d transition metals of the 4th period (iron, chromium or vanadium), including smelting, forging, cold reverse rolling to a degree of deformation of more than 95 % and recrystallization annealing at a temperature of ≥1000 ° C [RF Patent RU No. 2624564]. The method makes it possible to obtain a fourfold hardening of the substrate strip in comparison with strips of pure copper, while maintaining its non-magnetic properties and high sharpness of the crystallographic texture.

The closest analogue also does not solve the technical problem, including the expansion of the line of ternary alloys on a copper-nickel base, which have the necessary strength properties and the degree of sharpness of the crystallographic texture, while maintaining non-magnetic properties at the operating temperature of a high-temperature superconductor (77 K), used as epitaxial substrates. In addition, the 3d transition metals of the 4th period used in this method are less effective hardeners, per 1 at. % alloying element than, for example, the main refractory 4d-transition metals of the 5th period (niobium, molybdenum) and 5d-transition metals of the 6th period (tungsten).

The invention is based on the technical problem of expanding the range of ternary alloys on a copper-nickel base, having the necessary strength properties and a degree of sharpness of the crystallographic texture, while maintaining non-magnetic at the operating temperature of a high-temperature superconductor (77 K), inherent in substrates made of a ternary alloy on a copper-nickel based on the addition of iron, or chromium, or vanadium.

The technical problem is solved by achieving the technical result, which consists in expanding the arsenal of ternary alloys on a copper-nickel base, possessing the necessary strength properties and a degree of sharpness of the crystallographic texture, while maintaining non-magnetic at the operating temperature of a high-temperature superconductor (77 K), inherent in tapes-substrates made of ternary alloy on copper-nickel base with additions of iron, or chromium, or vanadium.

To create ternary copper-based alloys, in which a sharp cubic texture can be obtained, it is advisable to use alloys with a nickel content of not more than 45 at. %, since they are paramagnetic at the HTSC operating temperature (77 K).

Alloying a copper-nickel solid solution with some 4e-transition metals of the 5th period, such as niobium and molybdenum, as well as 5d-transition metals of the 6th period, such as tungsten, will make it possible to obtain the strength properties of the rolled strip no worse, even with a smaller amount of added additive, ( since the hardening ability of these metals per 1 at.% of the alloying element is higher than that of iron, chromium and vanadium) contained in the known ternary alloys based on copper-nickel.

The technical result is achieved by the fact that in the method of manufacturing a biaxially textured substrate from a ternary alloy on a copper-nickel base, including smelting, forging, cold reverse rolling of the strip to a degree of deformation of ≥97% and its recrystallization annealing at a temperature of ≥1000 ° C, according to the invention in as a ternary alloy on a copper-nickel base, an alloy with the addition of refractory 4d-transition metals of the 5th period or 5d-transition metals of the 6th period of the following chemical composition, at. %:

Niobium ≤2.5 at. %, or molybdenum ≤2.0 at. %, or tungsten ≤2.0 at. %,

Nickel - 40-45 at. %,

Copper is the rest;

In this case, the temperature of recrystallization annealing is 1000-1050 ° C.

Alloying a copper-nickel alloy with any of the listed elements: Nb, Mo, or W does not lead to a change in the type of deformation texture towards a decrease in the tendency to form a cubic recrystallization texture during alloy annealing.

It is known that when copper is doped with nickel, there is not a decrease in the energy of stacking faults (EDF), as when alloying copper with other metals, but even a slight increase in EDF [Gallagher P.C.J. The Influence of Alloying, Temperature, and Related Effects on the Stacking Fault Energy // Met. Trans. 1970. V.1. P. 2429-2460.], Which, in turn, leads to a change in the type of deformation texture towards an increase in the tendency to form a cubic texture of recrystallization during annealing of a double copper-nickel alloy. Complex alloying of copper with nickel and 3d-transition metal of 4 periods when creating a ternary alloy on a copper-nickel base in known ternary alloys on a copper-nickel base [RF Patent RU No. 2624564] also does not lead to a change in the type of deformation texture towards a decrease in the tendency to form cubic texture of recrystallization upon alloy annealing.

For all ternary alloys on a copper-nickel base with additions of 4d-transition metals of the 5th period (niobium, molybdenum) and 5d-transition metals of the 6th period (tungsten), the sum of the main deformation components C and S is more than twice the amount of component B and after recrystallization annealing at a temperature ≥1000 ° C in the rolled strips of these alloys, a sharp cubic texture is formed with the volume fraction of grains having an orientation {001} <100> ± 10 ° of more than 97% (Fig. 1).

We have established the optimum temperature of recrystallization annealing - 1050 ° C, which allows us to obtain a highly textured state in the strip of the studied ternary alloys approaching a single-crystal state. It was shown that with an increase in the recrystallization annealing temperature from 1000 ° C to 1050 ° C, the proportion of grains with a twin orientation decreases to less than 1%, and the structure also becomes more uniform in grain size (Fig. 2). Twin grains, present in small amounts after annealing at 1000 ° C, have characteristic "straight" boundaries (shown by arrows in Fig. 2a). After annealing at 1050 ° C, there are no twins in the structure of the studied alloys (Fig. 2b). An indicator of an increase in the quality of a cubic texture with an increase in the temperature of recrystallization annealing is a significant increase in the intensity level of the texture maximum (by ~ 30%), as well as a noticeably smaller area of the region on the pole figure, outlined by the contour of the highest intensity (Fig. 3).

The degree of perfection of the cubic texture of recrystallization of the ternary alloys Cu-Ni-W, Cu-Ni-Mo, Cu-Ni-Nb studied by us is shown in Fig. 1, and in table. 1.

An increase in the degree of textural and structural perfection of the ternary alloys Cu-Ni-W, Cu-Ni-Mo, Cu-Ni-Nb studied by us is shown in Fig. 2 and FIG. 3.

We analyzed the mechanical properties of textured tapes from the proposed ternary alloys, as well as to compare tapes from pure copper and known ternary alloys with iron, chromium and vanadium. Alloying the copper-nickel base with 4d-transition metals of the 5th period (niobium or molybdenum) or 5d-transition metals of the 6th period (tungsten) makes it possible to obtain an equivalent or higher hardening of the tape, while maintaining non-magnetic and the tendency of the known ternary alloys on a copper-nickel base to form a perfect cubic recrystallization texture. Replacing the third element of chromium, iron, or vanadium in the alloy with refractory elements niobium, molybdenum, or tungsten, which leads to a fourfold hardening of the pure copper substrate strip (Table 1), makes it possible to reduce the thickness of the substrate strip, which in turn leads to significant savings metal in the production of long cable.

We have established threshold values for the content of the alloying element (Nb, Mo or W) in ternary alloys on a copper-nickel basis, in weight. %: 0.5≤Nb≤2.5; 0.5≤Mo≤2.0; 0.5≤W≤1.1. When the content of the ternary copper-nickel-based alloy Cu-Ni-Me (Me = Cr, Fe, V) is less than 0.5 at. % of the alloying addition, the required level of strength of the substrate tape will not be achieved. On the other hand, the amount is more than 2.5 at. % niobium or more 2.0 at. % of molybdenum or tungsten in a ternary alloy on a copper-nickel base exceeds its limiting solubility in an fcc copper-nickel matrix, which can lead to the undesirable appearance of particles of the second phase and a decrease in the sharpness of the biaxial cubic texture.

Table 1 shows the chemical composition, mechanical properties and parameters of the cubic texture of the studied ternary alloys on a copper-nickel base in comparison with copper and ternary alloys with iron, chromium and vanadium.

FIG. 1 shows the EBSD orientation micromap (a), the component composition of the recrystallization texture (b), and the histograms of grain boundary misorientation (c) for the Cu-40% Ni-0.8% Mo alloy after annealing at 1050 ° C. The volume fraction of cubic grains with a scattering of ± 10 ° is more than 97%.

FIG. 2. shows the surface structure of textured ribbons made of p Cu-40% Ni - 0.8% Mo alloy after annealing at 1000 (a) and 1050 ° C (b).

FIG. 3 shows pole figures {111} for a textured ribbon made of Cu-40% Ni-0.8% W alloy after an hour of recrystallization annealing at 1000 (a) and 1050 ° C (b).

The method is carried out as follows:

Ternary alloys on a copper-nickel base are smelted in alundum crucibles in an argon atmosphere in a vacuum induction furnace. Use oxygen-free copper with a purity of 99.95 wt. %, nickel with a purity of 99.99 wt. %, as well as niobium, molybdenum and tungsten with a purity not lower than 99.94 wt. %. The ingots are forged at a temperature in the range of 1100-900 ° C into rods with a cross section of 10 × 10 mm. After grinding, blanks 10 × 10 × 150 mm are obtained, which are annealed at 650 ° C for 1.5 hours. The average grain size in the workpieces should not exceed 40 microns. Cold rolling of billets is carried out in two stages: stage 1 on a rolling mill with a roll diameter of 180 mm (deformation ~ 90%, the number of passes 35-40); Stage 2 - on a two-high rolling mill with polished rolls with a diameter of 55 mm to a strip with a thickness of 80-100 microns, the degree of cold deformation is 98-99%. Reversible rolling. Recrystallization annealing to obtain a biaxial texture is carried out for 1 hour in a vacuum oven (3⋅10 ^-5 mm Hg) at temperatures of 950, 1000, 1050, or 1100 ° C. Heating of strip samples, placed in a vacuum container, is carried out by planting in a furnace heated to the required temperature, cooling of the samples after annealing - outside the furnace space. After recrystallization annealing at a temperature of ≥1000 ° C, a sharp cubic texture with a volume fraction of grains having an orientation {001} <100> ± 10 ° of more than 97% is formed in the rolled strips of all alloys. Example 1.

Ni alloy - 40 at. %, Mo - 0.8 at. %, Cu - the rest, melted in an argon atmosphere in a vacuum induction furnace. We use oxygen-free copper with a purity of 99.95 wt. %, nickel with a purity of 99.99 wt. % and molybdenum with a purity not lower than 99.94 wt. %. An ingot weighing 500 g, forged at 1100-900 ° C onto a bar with a cross section of 10.5 × 10.5 mm. The resulting rod was ground to a size of 10 × 10 × 150 mm. Then, the obtained workpiece was annealed at a temperature of 650 ° C for 1.5 h to create a homogeneous fine-grained structure. The original grain size before cold rolling was 40 μm. Reverse rolling was carried out at room temperature. The degree of deformation was 99%, the final thickness of the tape was ~ 90 μm. The sum of the volume fractions of the deformation texture components was: S + C = 41.8%, 2 B = 25.1%. The sum of the volume fractions of the S and C components is much higher than the doubled volume fraction of the B component, which indicates the possibility of a sharp cubic texture in the ribbon after recrystallization annealing. As a result of recrystallization annealing in vacuum at a temperature of 1050 ° C for 1 h, a sharp cubic texture with the content of grains of orientation {001} <100> ± 100 ° ≥ 97% was formed in the alloy (see Fig. 1).

Ni alloy - 40 at. %, Mo - 0.8 at. %, Cu - the rest, has a high thermal resistance to the development of secondary recrystallization. The yield point of the finished strip is 108 MPa, (see Table 1), which is almost 4 times higher than the yield point of a pure copper strip and even slightly higher than the yield point of ternary alloys on a copper-nickel base with 3d transition metals of 4 periods: iron, or chromium, or vanadium (see table 1). The alloy is non-magnetic at the operating temperatures of a high-temperature superconductor.

Thus, the technical result has been achieved, which consists in expanding the arsenal of ternary alloys on a copper-nickel base, possessing the necessary strength properties, the degree of sharpness of the crystallographic texture, while maintaining non-magnetic at the operating temperature of a high-temperature superconductor (77 K), by means of which the posed technical problem is solved.

Claims (5)

1. A method of manufacturing a biaxially textured substrate in the form of a tape from a ternary alloy on a copper-nickel base for epitaxial deposition of buffer and high-temperature superconducting layers on it, including smelting with the introduction of an alloying element into a copper-nickel alloy to obtain an ingot of a ternary alloy on a copper-nickel base , forging an ingot into a billet in the form of a bar, cold reverse rolling of the billet to a degree of deformation of ≥97% to obtain a strip and recrystallization annealing of the resulting strip at a temperature of ≥1000 ° C, characterized in that when melting a ternary alloy on a copper-nickel base as an alloying element, niobium, or molybdenum, or tungsten is introduced and a ternary alloy is smelted, at. %: niobium ≤2.5, or molybdenum ≤2.0, or tungsten ≤2.0, nickel - 40-45, copper is the rest. 2. The method according to claim 1, characterized in that the temperature of the recrystallization annealing is 1000-1050 ° C.

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